Alloy



Patented Aug. 18,1925; UNITED ST E 1,550,509 PATENT ormer.

HUGH s. ooornn, or CLEVELAND, OHIO, ns srenon :iroxnnn'r LABORATORIES coiurANY, INC.; A conroiwrron OFNEW YORK.

K0 Drawing.

To all whom it may concern: 7

Be it known that I, HUGHQS. Coorna, citizen of the United States, 'residing' at Cleveland, in the county of Cuyahoga and- State of Ohio, have invented certain-new. and useful Improvements in Alloys, ot.

which the following is a specification;

This invention comprises alloys containing aluminum, iron, and a mallea'bili-zing agent, such as chromium. The alloys of the invention are characterized by 'a ratio of aluminum to iron which is so high that the" alloys would be unworkable if the malleabilizing constituent were omitted, butby virtue of the action of the malleabi'lizing constituent, the alloys can be forged, rolled and swaged when properly heated, provided the carbon content is sufficiently low, and can even be drawn mto wire. The alloys possess a very high electrical resistance and are stable at high temperatures, and are therefore admirably adapted for making resistance. elements.

- In my copending application, filed J a'nuary 24:, 1922, Serial No. 531,466, I have disclosed and claimed alloys of this 'type. The compositions of that application contain suflicient aluminum to give high electrical resistance as well as good resistance to oxidation at high temperatures, this aluminum content being so high with respect to the iron that the alloys would be unworkable in the absence of the malleabilizing constituent, as notedabove. An upper limit of about 16% aluminum was set, as this appears to cover the range wherein the desired properties are developed. As workability was found to decrease when the malleabilizing agent was increased beyond certain limits, compositions in which the percentage of malleabilizing constituent did not substantially exceed that of aluminum were indicated as preferable, and specifically claimed.

I have now found that by proper manipulation, compositions in which the malleabil-- izing agent substantially exceeds the aluminum are suflicientlyworkable for the purposes contemplated herein If the alloy contains, for example,.about 20% of chromium, with aluminum in the range indicated, the balance being iron, and

castings are made from it, the cast metal is crystalline and brittle, and appears entirely unsuitable for working. However, when the metal is heated to the range between Application filedol une'29,1923, Serial no. 648,581.

609 C. and 120 O C., it may be forged,

rolled or swag ed, and even drawn into Wire ofjsutiici'entflexibility. A minimal carbon content favors workability.

Alloys havingthe malleabilizing constitfuentpresentrin' excess of the aluminum display, likethe preferred compositions of my above mentioned copending application, extraordinary electrical resistances, in many instances exceeding 100 times that of cop- .er, and also exhibit the same satisfactory ehavior at high temperatures.

The temperature coetlicient of resistance is small and may be made zero, positive or negative by properadjustment of proportions. The following will vsufiiciently illustrate the effect of proportions on this coefficient. An alloy containing 12% A1, 19% Or, with the balance iron, has a coeflicient which is practically zero. Upon reducing the Al to 10%, the coefficient becomes definitely positive, while increasing the Al to 14% gives a negative coefiicient. An alloy contaimng 10% Al'and 25% Cr has a negative coefiicient whereas, as noted above, the coefficient of the alloy with 10% Al'and 19% Cr is positive.

It may be noted that the alloys of my invention possess the property of selective radiationywhen incandescent they register an abnormally high temperature on the optical pyrometer.

Alloys containing even more than 20% of chromium may be worked, particularly by swaging, but with difliculty as compared with alloys of lower chromium content. In my preferred compositions, the chromium is therefore not substantially in excess of 20%. An aluminum. content of 10-14% gives particularly good results.

Because it combines a practically zero temperature coefficient of resistance with other highly desirable qualities, an alloy containing about 12% Al and about 19% Cr, with the'balance predominantly iron, is the preferred composition of the group herein described.

While the ductility of the alloys of my invention is favorably affected by a very low carbon content, the casting of the low carbon material is somewhat diflicult. The metal does not become sufliciently fluid at the temperatures at which it is desirable to cast it, and for this reason the production of sound. castings is uncertain. Earthen more, the preparation of the .low-carbon alloy necessitates the use of low-carbon ma terials, such as ferrochromium and ferro poses contemplated. With carbon as high as 0.9%, the alloy can still be-fabricated into coarse wire, say one-eighth inch or more in diameter, while for the drawing of smaller wire, alloy of carbon content between 0.2% and 0.9% is suitable. With carbon below 0.35%, the alloy is sufficiently ductile for making resistance wire of any usual fineness. Hence, if the carbon is within the range of 0.2% to 0.35%, a combination of good casting and gooddrawing qualities is exhibited by the material.

I have also discovered another important and totally unexpected advantage arising from increasing the carbon above 0.2%. In the hot-working of the alloy by drawing or swaging, it is necessary to lubricate the material in order to prolong the life of the dies through which it is passed. The only lubricant available for this purpose is graphite. For some reason as yet unexplained, graphite clin s much more tenaciously to the metal WZIIBII- its carbon content is above 0.2%, and dies have a much longer life when used on such material than when used for working alloys of lower carbon content.

WVith the carbon content above about 0.9%, the alloy is no longer adapted for wire drawing by methods now practised industrially, but the casting qualities of this high carbon material ,are better than with alloy of any lower carbon content. Castings made from the high carbon alloy are sound, and the material is fine-grained and tough. Where drawing or swa ging are unnecessary, the carbon range 0.9% to 3% is preferred. 4

In making alloys of iron, aluminum and chromium, I have found that there is a strong and troublesome tendency for the aluminum to segregate unless it is alloyed with iron before being brought into contact with molten chromium or chromium alloy. To avoid the difficulty referred to, iron-aluminum alloy may be melted down with a ferrochromium, unalloyed iron being also added if necessary to secure the desired composition. An iron-aluminum alloy containing approximately equal per centages of the two metals is very conveniently used for the introduction of the aluminum into the final alloy, as the ironaluminum alloy of the composition designated is very brittle and therefore easily broken down into sizes convenient for weighing and melting.

This application is a continuation in part of my copending application Serial No. 581,246, filed August 11, 1922.

I claim:

1. An alloy consisting predominantly of iron, aluminum and chromium, the aluminum being within the range of 10% to 16%, and the chromium being in excess of the aluminum and not substantially in excess of 20%.

2. An alloy containing about 12% of aluminum and about 19% of chromium, with the balance predominantly iron.

3. An alloy consisting predominantly of iron, aluminum and chromium, and containing carbon; the aluminum being within the range of 10% to 16%, the chromium being in excess of the aluminum but,not substantially in excess of 20%, and the carbon forming at least 0.2% and not more than about 3% of the alloy.

4. An alloy consisting predominantly of iron, aluminum and chromium, and containing carbon; the aluminum being within the range of 10% to 16%, the chromium being in excess of the aluminum but not substantially in excess of 20%, and the carbon forming at least 0.2% and not more than about 0.9% of the alloy. 5. An alloy consisting predominantly of iron, aluminum and chromium, and containing carbon; the aluminum being within the range of 10% to 16%, the chromium being in excess of the aluminum but not substantially in excess of 20%, and the carbon forming at least 0.2% and not more than 0.35% of the alloy.

6. An alloy containing about 12% of aluminum and about 19% of chromium, with the balance predominantly iron, and containing carbon in quantity not less than 0.2% and not greater than about 0.9%.

7. An alloy containing about 12% of aluminum and about 19% of chromium, with the balance predominantly iron, and containing carbon in quantity not less than 0.2% and not greater than about 0.35%.

8. Process of making iron, aluminum, and iron-aluminum-chromium alloys, which comprises forming the aluminum to be used into a binary ferrous alloy, and then incorporating the chromium.

9. Process accordin to claim 8 in which the binary alloy containing the aluminum is 

